1. Field of the Invention
The present invention relates to a high frequency module including a high frequency amplifier circuit and an LC circuit.
2. Description of the Related Art
High frequency modules have advantages in downsizing, integration, and the like, and thus are currently embedded in widely prevailing wireless communication devices such as cellular phones and the like. For example, as one kind of the high frequency modules, examples thereof include a high frequency module that is composed of a filter circuit, a matching circuit, an amplifier circuit, and the like, and is used for transmitting and receiving signals. Conventional high frequency modules are, for example, described in Japanese Unexamined Patent Application Publication No. 2006-121147, Japanese Unexamined Patent Application Publication No. 2005-123909, and Japanese Unexamined Patent Application Publication No. 2005-166980.
The high frequency modules described in Japanese Unexamined Patent Application Publication No. 2006-121147 and Japanese Unexamined Patent Application Publication No. 2005-123909 are each provided with a multilayer substrate, a high frequency amplifier circuit, a thermal via, and a filter circuit. The high frequency amplifier circuit is mounted on the multilayer substrate. The thermal via is formed in the multilayer substrate directly below the high frequency amplifier circuit and penetrates through the multilayer substrate. The filter circuit is composed of a surface acoustic wave (SAW) filter that uses a SAW element, and is mounted near the high frequency amplifier circuit.
The high frequency module described in Japanese Unexamined Patent Application Publication No. 2005-166980 is, as is the case with Japanese Unexamined Patent Application Publication No. 2005-123909, provided with a multilayer substrate, a high frequency amplifier circuit, a thermal via, and a filter circuit. The high frequency amplifier circuit is mounted on the multilayer substrate. The thermal via is formed in the multilayer substrate directly below the high frequency amplifier circuit, and penetrates through the multilayer substrate. The filter circuit of Japanese Unexamined Patent Application Publication No. 2005-166980 is an LC filter circuit in which an inductor and a capacitor are combined. The inductor and the capacitor are each formed of electrode patterns formed in the multilayer substrate near the thermal via.
In the cases of the high frequency modules described in Japanese Unexamined Patent Application Publication No. 2006-121147 and Japanese Unexamined Patent Application Publication No. 2005-123909, it is necessary to secure a space for mounting the SAW filter on the multilayer substrate in order to mount the SAW filter on the multilayer substrate.
In the case of the high frequency module described in Japanese Unexamined Patent Application Publication No. 2005-166980, the LC filter circuit is formed inside the multilayer substrate. However, the LC filter circuit cannot be formed directly below the high frequency amplifier circuit since the thermal via is provided directly below the high frequency amplifier circuit. Therefore, it is necessary to secure a space in the multilayer substrate to form the LC filter circuit.